If you first domain controller within a domain was running Windows Server 2008 or later you should be using DFS-R (Distributed File System Replication). If you upgraded from Windows 2003 domain, there is a big chance that you are still using FRS (File Replication Service).
To be sure, run following command on one of your DCs:
dfsrmig /getmigrationstate
If response is "Start" it means you are using FRS
If response is "Eliminated" it means you are using DFS-R
The response indicates the state of FRS to DFS-R migration process. Following states are possible:
0 - "START"
1 - "PREPARED"
2 - "REDIRECTED"
3 - "ELIMINATED"
Windows Server 2008 and later
